Stabilized zirconia (i.e., stabilized zirconium oxide), e.g., yttria stabilized zirconia and lanthana stabilized zirconia, is commonly employed as a catalyst support, particularly for partial oxidation fuel reforming. Generally, rhodium supported stabilized tetragonal zirconia's are exclusively preferred.
The tetragonal stabilized zirconia is typically used to form a washcoat for supporting catalytic active metals or metal oxides. This washcoat has been used to increase dispersion of the active ingredients, and therefore to increase their utilization and stability. The washcoat is placed onto a substrate, such as a monolith, foam, or the like, which is then disposed in a housing.
Partial oxidation fuel reforming reactions typically proceed at very high temperatures, usually in excess of 1,000° C. The highest temperatures (even exceeding 1,100° C.) can be reached due to heat released during transient operations, system upsets, or deliberately when high flow rates are required, or when operating in a mode where heat lost via conduction, radiation, or convection, is less than the amount of heat generated by the reaction. Under these circumstances, typical washcoat materials (e.g., tetragonal stabilized zirconia) tend to fail. The failure modes involve one or more of melting, recrystallization, sintering, collapse of pore structure, loss of surface area, etc. In all of these cases, changes to the washcoat result in a reduction of the amount of active ingredients available for the reaction, thus reducing the effectiveness of the catalyst. Thus there is a need to provide a more stable washcoat material.